1. Field of the Invention
The present invention relates to an apparatus having a position detecting apparatus used with a correction lens, for example, a camera having an optical shake correction apparatus in order to control a position of the correction lens thereby for reducing an influence of vibrations of relatively low frequency due to an unintentional hand movement called camera shake.
2. Description of the Related Art
This type of position detecting apparatus is described below by taking a camera having an optical shake correction device as an example.
In the camera, unintentional hand movement (camera shake) is detected by a vibration sensor detecting an angular acceleration, angular velocity and so on. The correction lens is moved corresponding to a value of sensing signal from the vibration sensor in order to cancel the movement of an optical axis of a taking lens of the camera. In such a camera, it is necessary to detect the position of the optical axis of the correction lens accurately in the movement of the correcting lens for accurately performing the above correction.
In a conventional position detecting device for an optical shake correction device, shown in the publication gazette of Japanese Unexamined Patent Application Hei 4-18515, an LED serving as a light emitting device and a PSD (Position sensitive light Detector) serving as light receiving device are respectively provided on a moving portion and a fixed portion. The center of a light beam spot emitted from the LED is detected by the PSD. Thus, the position of the moving portion is known.
FIG. 12A illustrates a structure of a conventional optical shake correction device. FIG. 12B illustrates a relation between a slit of a light emitting portion and a light receiving surface of a light receiving portion in a position detecting device of the mechanism when an axis designated by arrow Y is parallel with the slit. FIG. 12C illustrates another relation between the slit and the light receiving surface when the axis designated by arrow Y and the slit are deviated from the parallel state.
As can be seen from FIG. 12A, a correction lens group 61 is held at the center of a frame 62. A first position sensor 63 and a second position sensor 64 are provided on the frame 62 so as to cross at right angle. The first position sensor 63 detects a position of the correction lens group 61 in a direction shown by arrow X (hereinafter abbreviated as X-direction). The second position sensor 64 detects a position of the correction lens group 61 in a direction designated by arrow Y (hereinafter abbreviated as Y-direction). The frame 62 is moved a predetermined distance in X-direction by an X-direction driving mechanism (not shown in the figure) responding to an information detected by the first position sensor 63 in order to correct the displacement of an optical axis of a taking lens due to the camera shake in X-direction. Similarly, the frame 62 is moved a predetermined distance in Y-direction by a Y-direction driving mechanism 65 responding to an information detected by the second position sensor 64 in order to correct the displacement of an optical axis of a taking lens due to the camera shake in Y-direction.
A pair of an LED 66 serving as a light emitting device and a PSD 67 serving as a light receiving device is provided on respective of the first and second position sensors 63 and 64. Each LED 66 faces the PSD 67 through a slit 68. The light emitting portion consists of the LED 66 and the slit 68 is relatively movable against the PSD 67 serving as the light receiving portion. Thus, the positions of the correction lens group 61 in X-direction and Y-direction can be detected.
When the camera shake occurs, a vertical camera shake component is corrected by moving the correction lens group 61 in X-direction which is controlled by the position information from the first position sensor 63 and a horizontal camera shake component is corrected by moving the correction lens group 61 in Y-direction which is controlled by the position information from the second position sensor 64. Thus, the movement of the optical axis of the taking lens of the camera due to the camera shake is substantially canceled by the movement of the optical axis of the correction lens group, so that shake of an image focused on a focal plane of the camera is reduced.
However, in the above-mentioned conventional structure, the LED 66 is constituted so as to be movable in both of X-direction and Y-direction to the light receiving surface of the PSD 67. A moving component in a direction which is not in a position detecting direction (that is, Y-direction when the position sensing is performed in X-direction or X-direction when the position sensing is performed in Y-directional) causes a deviation in the center of the light beam spot emitted from the LED 66 and passing through the slit 68 on the light receiving surface of the PSD 67. The deviation further causes an error component of the position detection, so that it is difficult to detect the position of the correction lens group accurately.
As can be seen from FIG. 12B, when the position detection is performed along X-direction and the lengthwise direction of the slit 68 is parallel with Y-direction, the position of the center of the light beam spot on the light sensing surface of the PSD 67, which is emitted from the LED 66 and passing through the slit 68, may not deviate in X-direction, even though the LED 66 and the slit 68 move in Y-direction. However, the LED 66 and the slit 66 really move in both of X-direction and Y-direction. Furthermore, there are tolerances in each element. Thus, as can be seen from FIG. 12C, the lengthwise direction of the slit 68 slightly tilts from Y-direction. When the LED 66 and the slit 68 move in Y-direction, a deviation component A of the center of the light beam spot on the light receiving surface of the PSD 67, which is emitted from the LED 66 and passing through the slit 68, occurs in X-direction. The deviation component A causes the error component of the position detection and is included in the position detection of the correction lens group 61 in X-direction.